Tissue products having substantially equal machine direction and cross-machine direction mechanical properties

ABSTRACT

A tissue product having a combination of substantially equal tensile energy absorbed (TEA) in the machine direction and the cross-machine direction of the tissue sheet and a significant level of stretch in both directions provides improved perception of strength and resistance to “poke through” in use.

BACKGROUND OF THE INVENTION

In the field of tissue products, such as facial tissue, bath tissue,table napkins, paper towels and the like, the tensile strength of thesesheet products is often measured as the geometric mean tensile strength,which takes into account the machine direction (MD) tensile strength andthe cross-machine direction (CD) tensile strength. The geometric meantensile strength is calculated as the square root of the product of theMD and CD tensile strengths. However, using a single strength value tocharacterize a sheet can be misleading because the MD and CD tensilestrength values are typically very different, with the MD tensilestrength being much greater than the CD tensile strength. In use, theproduct is more likely to fail because its strength is limited by theweakest link, namely the CD tensile strength. In response, some prioremphasis has been made on making products in which the machine direction(MD) and cross direction (CD) tensile strengths of the sheets are thesame, thereby eliminating sheet failure caused by a relatively weak CDtensile strength. Tissue sheets having equal MD and CD tensile strengthsare typically referred to as being a “square” sheet. However, focusingon tensile strength alone ignores the key role that other propertiesplay in the consumer's perception of strength. Therefore there is a needfor a tissue sheet in which the perceived in-use strength is improved.

SUMMARY OF THE INVENTION

It has now been discovered that the perceived in-use strength of atissue product can be improved by providing the product with one or moretissue sheets (plies) having substantially equal MD and CD tensileenergy absorbed (TEA) (hereinafter defined) and a significant level ofstretch, particularly in the CD direction of the sheet. Thesubstantially equal TEA in combination with good stretch correlates withimproved poke-through resistance for the tissue product, which isparticularly important for bath tissue, but can be equally beneficialfor facial tissue and towels.

Hence, in one aspect the invention resides in a tissue sheet having athree-dimensional surface topography, an MD/CD TEA ratio of from about0.8 to about 1.2, more specifically from about 0.9 to about 1.1, stillmore specifically about 1.0, and a CD stretch of about 5 percent orgreater. For purposes herein, a “three-dimensional surface topography”is a surface having regularly repeating elevated and relativelydepressed regions having an average z-directional elevation differenceof about 0.5 millimeter or greater, more specifically about 0.6millimeter or greater, more specifically about 0.7 millimeter orgreater, still more specifically about 1.0 millimeter or greater. Thethree-dimensional surface topography serves to provide the tissue sheetwith the necessary level of stretch and/or CD strength.

More specifically, the invention resides in a tissue sheet having athree-dimensional surface topography, an MD/CD TEA ratio of from about0.8 to about 1.2, a CD stretch of about 5 percent or greater, an MDstretch of about 5 percent or greater and a geometric mean tensilestrength of about 1500 grams or less per 3 inches of width.

The MD and CD tensile strengths of the sheets of this invention can beabout 600 grams or greater per 3 inches of sample width, morespecifically about 700 grams or greater per 3 inches of sample width,more specifically about 800 grams or greater per 3 inches of samplewidth, more specifically about 900 grams or greater per 3 inches ofsample width, and still more specifically about 1000 grams or greaterper 3 inches of sample width.

The geometric mean tensile strength of the sheets of this invention canbe about 1500 grams or less per 3 inches of width, more specificallyabout 1200 grams or less per 3 inches of width and still morespecifically from about 500 to about 1200 grams per 3 inches of width.

The MD stretch for the sheets of this invention can be about 3 percentor greater, more specifically about 5 percent or greater, morespecifically from about 3 to about 30 percent, more specifically fromabout 3 to about 25 percent, more specifically from about 3 to about 15percent, and still more specifically from about 3 to about 10 percent.The CD stretch for the sheets of this invention can be about 5 percentor greater, more specifically about 10 percent or greater, morespecifically from about 5 to about 20 percent, more specifically fromabout 5 to about 15 percent, and still more specifically from about 5 toabout 10 percent. Because the CD stretch of the sheets of this inventioncan be substantially increased by various factors, primarily includinghighly three-dimensional fabrics, and because the MD stretch can bereduced by various factors in order to make the MD TEA and CD TEAsubstantially equal, in many cases the CD stretch of the sheets of thisinvention will be greater than the MD stretch.

The geometric mean TEA can be about 20 gram-centimeters or less persquare centimeter, more specifically about 10 gram-centimeters or lessper square centimeter, more specifically from about 2 to about 8gram-centimeters per square centimeter and still more specifically fromabout 2 to about 4 gram-centimeters per square centimeter.

The basis weight of the tissue sheets of this invention can be fromabout 10 to about 45 grams per square meter (gsm), more specificallyfrom about 10 to about 35 gsm, still more specifically from about 20 toabout 35 gsm, more specifically from about 20 to about 30 gsm and stillmore specifically from about 30 to about 35 gsm.

The tissue sheets of this invention can be layered or non-layered(blended). Layered sheets can have two, three or more layers. For tissuesheets that will be converted into a single-ply product, it can beadvantageous to have three layers with the outer layers containingprimarily hardwood fibers and the inner layer containing primarilysoftwood fibers. Tissue sheets in accordance with this invention wouldbe suitable for all forms of tissue products including, but not limitedto, bathroom tissue, kitchen towels, facial tissue and table napkins forconsumer and services markets.

Furthermore, to be commercially advantaged, it is desirable to minimizethe presence of pinholes in the sheet. The degree to which pinholes arepresent can be quantified by the Pinhole Coverage Index, the PinholeCount Index and the Pinhole Size Index, all of which are determined byan optical test method known in the art and described in U.S. PatentPublication No. US 2003/0157300 A1 entitled “Wide Wale Tissue Sheets andMethod of Making Same”, published Aug. 21, 2003, which is hereinincorporated by reference. More particularly, the “Pinhole CoverageIndex” is the arithmetic mean percent area of the sample surface area,viewed from above, which is covered or occupied by pinholes. Forpurposes of this invention, the Pinhole Coverage Index can be about 0.25or less, more specifically about 0.20 or less, more specifically about0.15 or less, and still more specifically from about 0.05 to about 0.15.The “Pinhole Count Index” is the number of pinholes per 100 squarecentimeters that have an equivalent circular diameter (ECD) greater than400 microns. For purposes of this invention, the Pinhole Count Index canbe about 65 or less, more specifically about 60 or less, morespecifically about 50 or less, more specifically about 40 or less, stillmore specifically from about 5 to about 50, and still more specificallyfrom about 5 to about 40. The “Pinhole Size Index” is the meanequivalent circular diameter (ECD) for all pinholes having an ECDgreater than 400 microns. For purposes of this invention, the PinholeSize Index can be about 600 or less, more specifically about 500 orless, more specifically from about 400 to about 600, still morespecifically from about 450 to about 550. By way of example, currentcommercially available Charmin® bathroom tissue has a Pinhole CoverageIndex of from 0.01-0.04, a Pinhole Count Index of from 250 -1000, and aPinhole Size Index of 550-650.

Suitable papermaking processes useful for making tissue sheets inaccordance with this invention include uncreped throughdrying processeswhich are well known in the tissue and towel papermaking art. Suchprocesses are described in U.S. Pat. No. 5,607,551 issued Mar. 4, 1997to Farrington et al., U.S. Pat. No. 5,672,248 issued Sep. 30, 1997 toWendt et al. and U.S. Pat. No. 5,593,545 issued Jan. 14, 1997 toRugowski et al., all of which are hereby incorporated by reference.Throughdrying processes with creping, however, can also be used.

In the interests of brevity and conciseness, any ranges of values setforth in this specification contemplate all values within the range andare to be construed as support for claims reciting any sub-ranges havingendpoints which are whole number values within the specified range inquestion. By way of a hypothetical illustrative example, a disclosure inthis specification of a range of from 1 to 5 shall be considered tosupport claims to any of the following ranges: 1-5; 1-4; 1-3; 1-2; 2-5;2-4; 2-3; 3-5; 3-4; and 4-5.

Test Procedures

Tensile strengths and related parameters are measured using a crossheadspeed of 254 millimeters per minute, a full scale load of 4540 grams, ajaw span (gauge length) of 50.8 millimeters and a specimen width of 762millimeters. The MD tensile strength is the peak load per 3 inches ofsample width when a sample is pulled to rupture in the machinedirection. Similarly, the CD tensile strength represents the peak loadper 3 inches of sample width when a sample is pulled to rupture in thecross-machine direction. For 1-ply products each tensile strengthmeasurement is done on 1-ply. For multiple ply products tensile testingis done on the number of plies expected in the finished product. Forexample, 2-ply products are tested two plies at one time and therecorded MD and CD tensile strengths are the strengths of both plies.The same testing procedure is used for samples intended to be more thantwo plies.

More particularly, samples for tensile strength testing are prepared bycutting a 3 inches (76.2 mm) wide×5 inches (127 mm) long strip in eitherthe machine direction (MD) or cross-machine direction (CD) orientationusing a JDC Precision Sample Cutter (Thwing-Albert Instrument Company,Philadelphia, Pa., Model No. JDC 3-10, Serial No. 37333). The instrumentused for measuring tensile strengths is an MTS Systems Sintech 11S,Serial No. 6233. The data acquisition software is MTS TestWorks® forWindows Ver. 3.10 (MTS Systems Corp., Research Triangle Park, N.C.). Theload cell is selected from either a 50 Newton or 100 Newton maximum,depending on the strength of the sample being tested, such that themajority of peak load values fall between 10 and 90% of the load cell'sfull scale value. The gauge length between jaws is 4+/−0.04 inches(101.6+/−1 mm). The jaws are operated using pneumatic-action and arerubber coated. The minimum grip face width is 3 inches (76.2 mm), andthe approximate height of a jaw is 0.5 inches (12.7 mm). The crossheadspeed is 10+/−0.4 inches/min (254+/−1 mm/min), and the break sensitivityis set at 65%. The sample is placed in the jaws of the instrument,centered both vertically and horizontally. The test is then started andends when the specimen breaks. The peak load is recorded as either the“MD tensile strength” or the “CD tensile strength”of the specimendepending on the sample being tested. At least six (6) representativespecimens are tested for each product, taken “as is”, and the arithmeticaverage of all individual specimen tests is either the MD or CD tensilestrength for the product.

In addition to tensile strength, the stretch, tensile energy absorbed(TEA), and slope are also reported by the MTS TestWorks® for WindowsVer. 3.10 program for each sample measured. Stretch (either MD stretchor CD stretch) is reported as a percentage and is defined as the ratioof the slack-corrected elongation of a specimen at the point itgenerates its peak load divided by the slack-corrected gauge length.Slope is reported in the units of grams (g) and is defined as thegradient of the least-squares line fitted to the load-corrected strainpoints falling between a specimen-generated force of 70 to 1.57 grams(0.687 to 1.540 N) divided by the specimen width.

Total energy absorbed (TEA) is calculated as the area under thestress-strain curve during the same tensile test as has previouslydescribed above. The area is based on the strain value reached when thesheet is strained to rupture and the load placed on the sheet hasdropped to 65 percent of the peak tensile load. Since the thickness of apaper sheet is generally unknown and varies during the test, it iscommon practice to ignore the cross-sectional area of the sheet andreport the “stress” on the sheet as a load per unit length or typicallyin the units of grams per 3 inches of width. For the TEA calculation,the stress is converted to grams per centimeter and the area calculatedby integration. The units of strain are centimeters per centimeter sothat the final TEA units become g-cm/cm².

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic flow diagram of a tissue making process useful formaking tissues in accordance with this invention.

FIG. 2 is a schematic plot of a stress/strain curve to the breakingpoint (MD and CD) for a typical tissue sheet.

FIGS. 3A and 3B show schematic plots of stress/strain curves to thebreaking point for different tissue sheets in accordance with thisinvention.

FIGS. 4-10 are plots of data generated by Examples 2-42. Specifically,FIG. 4 is a plot of the MD/CD TEA Ratio versus the MD/CD Tensile Ratio.

FIG. 5 is the same plot as that of FIG. 4, but identifying the transferfabric and throughdrying fabric used to produce the sheets of thisinvention.

FIG. 6 is a plot of the MD/CD TEA ratio versus MD stretch, illustratingthe effect of different transfer fabrics and throughdrying fabrics.

FIG. 7 is a plot of the MD/CD TEA ratio versus the percent rushtransfer.

FIG. 8 is a plot of the MD/CD TEA ratio versus CD stretch for thedifferent transfer fabric and throughdrying fabric combinations.

FIG. 9 is a plot of the MD TEA versus the percent rush transfer.

FIG. 10 is a plot of the CD TEA versus the percent rush transfer.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIG. 1, shown is an uncreped throughdried tissue makingprocess in which a multi-layered headbox 5 deposits an aqueoussuspension of papermaking fibers between forming wires 6 and 7. Thenewly-formed web is transferred to a slower moving transfer fabric 8with the aid of at least one vacuum box 9. The level of vacuum used forthe web transfers can be from about 3 to about 15 inches of mercury (76to about 381 millimeters of mercury), preferably about 10 inches (254millimeters) of mercury. The vacuum box (negative pressure) can besupplemented or replaced by the use of positive pressure from theopposite side of the web to blow the web onto the next fabric inaddition to or as a replacement for sucking it onto the next fabric withvacuum. Also, a vacuum roll or rolls can be used to replace the vacuumbox(es).

The web is then transferred to a throughdrying fabric 15 and passed overthroughdryers 16 and 17 to dry the web. The side of the web contactingthe throughdrying fabric is referred to herein as the “fabric side” ofthe web. The opposite side of the web is referred to as the “air side”of the web. While supported by the throughdrying fabric, the web isfinal dried to a consistency of about 94 percent or greater. Afterdrying, the sheet is transferred from the throughdrying fabric to fabric20 and thereafter briefly sandwiched between fabrics 20 and 21. Thedried sheet remains with fabric 21 until it is wound up at the reel 25.Thereafter, the tissue sheet can be unwound, calendered and convertedinto the final tissue product, such as a roll of bath tissue, in anysuitable manner.

The various fabrics, particularly the throughdrying fabric and thetransfer fabric, have a topographical structure that impartsthree-dimensionality to the resulting tissue sheet or ply. Thisthree-dimensionality in turn imparts CD stretch to the sheet because thethree-dimensional bumps and/or ridges can be pulled out when the sheetis stressed. The MD stretch is also enhanced in part by thethree-dimensionality, but to a greater extent the MD stretch is providedby the “rush” transfer of the newly-formed web from the faster movingforming fabric to the slower moving transfer fabric, or by creping ifpresent.

Suitable three-dimensional fabrics useful for purposes of this inventionare those fabrics having a top surface and a bottom surface. During wetmolding and/or throughdrying, the top surface supports the wet tissueweb. The wet tissue web conforms to the top surface and during moldingis strained into a three-dimensional topographic form corresponding tothe three-dimensional topography of the top surface of the fabric.Adjacent the bottom face, the fabric has a load-bearing layer whichintegrates the fabric and provides a relatively smooth surface forcontact with various tissue machine elements.

The transfer and TAD fabrics used within have textured sheet contactingsurfaces comprising of substantially continuous machine-direction ridgesseparated by valleys and are similar to those described in U.S. Pat. No.2003/0157300 A1 issued on Aug. 21, 2003 to Burazin et al. Furthermore,such fabrics with ridged sculpted layers can be extended to include aheight of ridges from 0.4 mm to about 5 millimeters, a ridge width of0.5 mm or greater, and the frequency of occurrence of the ridges in thecross-machine direction of the fabric from about 1.5 to 8 percentimeter. Specific fabric styles described in this manner and includedin the examples include Voith Fabrics t1205-1, t1207-6, t1203-1, andt1203-8.

Other suitable fabrics with topographical features are described by U.S.Pat. No. 5,429,686 issued on Jul. 4, 1995 to Chiu et al., of whichfabric style Voith Fabrics t807-1 is one embodiment. Additionaltopographical fabrics with MD dominant features which can be utilizedare described in U.S. Pat. No. 2003/0084953 A1 issued on May 8, 2003 toBurazin et al.

Fabrics can be woven or non-woven, or a combination of a woven substratewith an extruded sculpture layer provided the topographical sculpturedlayer. Fabrics may also be finished so the warps are parallel to thecross-machine direction when run on a tissue machine, creating a seriesof substantially continuous cross-machine direction ridges separated byvalleys.

Other fabrics suitable for use as the transfer fabric or the TAD fabriccan have textured sheet contacting surfaces comprising of a waffle-likepattern consisting of both machine-direction and cross-machine directionridges with sculpted layers which have a peak height (from lowestelement contacted by the tissue to the highest element) ranging from 0.5mm to about 8 millimeters, and a frequency of occurrence of thetwo-dimensional pattern from about 0.8 to about 3.6 per squarecentimeter of fabric.

FIG. 2 illustrates MD and CD stress/strain curves for a typical tissuesheet having MD dominant topographical features. The MD curve may have ahigher slope than the CD curve for a number of reasons, including fabrictopography and fiber orientation. As shown, tissue sheets typically havegreater strength in the MD and also greater stretch. One can see fromthese two curves that the area under the MD curve (the MD TEA) isgreater than the area under the CD curve (the CD TEA).

The macro-structure of tissue often has a significant influence on thephysical properties of the tissue. For example, when tissue is producedwith MD-dominant topographic features, the result is often an increasein CD stretch relative to flat tissue, and a modification in the shapeof the tensile stress-strain relationship. The relatively low stress atlow strain for the CD curve is due to the low stress required to “pullout” the topography. The difference in shape between the MD and CDstress-strain curves is often a major reason for CD TEA deficiency.

Another factor affecting the shape of the MD and CD stress-strain curvesis fiber orientation. Most paper products, including tissue, have morefibers oriented in the MD than the CD. Consequently, the MDstress-strain curve for flat (non-three-dimensional) tissue tends to beconvex as the one depicted in FIG. 2. For these reasons, even whentissue is produced with equal MD and CD strength and equal MD and CDstretch, the shape difference between the stress-strain curves causesthe MD/CD TEA ratio to be much greater than one.

FIGS. 3A and 3B show two possible variations of the curves of FIG. 2that represent tissue sheets of this invention. As shown, the solid linerepresents the MD tensile curve and the dashed line represents the CDtensile curve. In FIG. 3A, the dashed line represents one way ofachieving a tissue sheet of this invention, which is to impart a higherdegree of stretch into the CD of the sheet. By so doing, the area underthe curve is increased relative to that shown in FIG. 2, such that theMD/CD TEA approaches unity. The dashed line in FIG. 3B representsanother way of achieving a tissue sheet in accordance with thisinvention, in which the MD and CD stress/strain curves are more equal.This can be achieved by providing CD-dominant topographic features(features that are primarily oriented in the CD) through the use ofthree-dimensional throughdrying fabrics. In such cases, the stress atlow strain values is decreased for the MD curve relative to that of FIG.2 due to “pulling out” of the topography. Conversely, the stress at lowstrain for the CD curve is increased because the molded topographicfeatures do not pull out as easily. Thus, sheets made in such a mannerwould have an MD/CD TEA ratio that is lower than sheets made with flator MD-dominant topographic features.

FIG. 4 illustrates the relationship between the MD/CD TEA ratio andMD/CD Tensile ratio. The MD/CD Tensile ratio was controlled by headboxconditions and rush transfer. The primary control variable for fiberorientation was the rheology of the slurry exiting the slice. The pilotpaper machine used to manufacture these materials was a rush former. Assuch, the pulp slurry exiting the headbox slice was traveling at ahigher velocity than the forming wire. To decrease the MD/CD ratio, theslice was opened to maximum gap, thereby flooding the forming zone tominimize the rush of slurry onto the slower-moving forming fabric. Inmost cases, the forming zone was flooded to an extent that producedturbulent flow conditions during forming. Typical commercial papermachines are able to control the MD/CD tensile ratio without turbulentflow due to more complex control systems. It is important to note thatthere is not direct correlation between MD/CD TEA ratio and MD/CDTensile ratio, or further that it is not possible to infer the MD/CD TEAratio given information on MD/CD ratio and MD/CD stretch.

FIG. 5 illustrates the significant effect on the strength properties ofthe sheet as a function of the transfer and through-air-drying (TAD)fabrics used. By applying topographic transfer fabrics, samples madefrom several fabric combinations achieved MD/CD TEA values near 1.0 fora wide range of MD/CD Tensile ratios. As a means of illustration, thet1205-1 fabric has 3.02 ripples/cm and a ridge height of approximately0.8 mm. The t1203-1 fabric has 2.03 ripples/cm and a ridge height ofapproximately 1.1 mm.

FIG. 6 illustrates the relationship between MD stretch and TEA Ratio forthe samples of this invention produced in the Examples. While the MD TEAgenerally increases when the MD stretch increases, this relationship wasnot observed for the samples produced. Instead, the samples of thisinvention having a substantially equal MD/CD TEA ratio were producedover a wide range of MD stretch. The MD stretch was controlled by rushtransfer between the forming fabric and transfer fabric. No attempt wasmade to remove MD stretch by increasing draw at the reel. The greatertopography (higher CD strain) transfer fabric (t1203-1) allowed for anincrease in MD stretch while maintaining an MD/CD TEA ratio near one.The trend of obtaining higher stretch with greater topography (CDstrain) transfer fabric, at an MD/CD ratio of approximately 1, would beexpected to continue with the use of transfer fabrics having greatertopography than that of the t1203-1 fabric. Examples of such fabricswould be the Voith Fabrics t1203-4 and the t1203-6, which both havehigher ridge height than the t1203-1.

FIG. 7 illustrates the effect of rush transfer between the formingfabric and the transfer fabric on the MD/CD TEA ratio. As shown, theMD/CD TEA ratio was constant over a wide range of rush transfer level.Additionally, increasing transfer fabric topography from t1205-1 tot1203-1 allowed for higher levels of rush transfer while maintaining alow MD/CD TEA ratio.

FIG. 8 depicts the relationship between MD/CD TEA ratio and CD stretch.CD stretch appears to have little impact on the MD/CD TEA ratio.Therefore sheets of the invention can be produced over a wide range ofCD stretch values. It can be noted that higher topographical fabrics(t1203-1 as compared to the t1205-1) allow for higher CD Stretch andhigher MD stretch (FIG. 6) at equivalent-MD/CDTEA ratio. Using evenhigher topographical fabrics in the transfer position would allow foreven higher MD and CD stretch at an MD/CD TEA ratio of one.

FIG. 9 illustrates the relationships between MD TEA and rush transferfor the two fabric combinations used in these examples. Within acombination of fabrics, the MD TEA increases slightly with increasingRush Transfer. Rush transfer was found to have a direct and inverseeffect on MD stretch and strength. Specifically, as rush transferincreases, MD stretch increases, and MD strength decreases. The rushtransfer level at which MD TEA is optimized depends on the transfer andTAD fabrics used.

FIG. 10 illustrates the relationships between CD TEA and rush transferfor the two fabric combinations used in these examples. Within acombination of fabrics, the CDTEA increases slightly with increasingRush Transfer.

EXAMPLES Example 1 Hypothetical

The need for significant stretch (about 5 percent or greater) is animportant factor for purposes of this invention because it is relativelyeasy to remove stretch and lower tensile strength in the MD to makethose properties equal to the stretch and tensile strength in the CD,thereby resulting in an equal or substantially equal MD TEA and CD TEA.However, since stretch and strength are much more difficult to generatein the CD, merely making these properties equal would only provide aweak sheet with low stretch with little or no consumer benefit. Toillustrate this point, hypothetical products are listed in Table 1 belowshowing the effect of their properties on TEA. TABLE 1 MD CD MD TensileTensile Stretch CD MD TEA CD TEA Product g/3″ g/3″ % Stretch % g-cm/cm²g-cm/cm² A 1000 800 15 5 9.8 2.6 B 800 800 5 5 2.6 2.6 C 800 800 10 105.2 5.2

The hypothetical examples are assumed to have a linear stress-straincurve which is not usually the case for tissue products, which havestress-strain curves with varying shapes depending on the method ofmanufacture and the specific fabrics and chemicals used to impartstretch and strength to the product. However, using a linearstress-strain curve allows a direct calculation of the tensile energyabsorbed to better illustrate the usefulness of this invention. Notethat it is not possible to directly calculate TEA for real products fromthe strength and stretch properties where the shape of the stress-straincurve is not known. However, this example serves to illustrate that asubstantially equal MD TEA and CD TEA is a useful property that cannotbe inferred directly from strength properties.

Referring to Table 1, product “A” is a typical product made today wherethe MD tensile and stretch is higher than the CD tensile and stretch.Since the MD and CD TEAs are products of tensile and stretch, the MD TEAis almost four times that of the CD TEA. The product would fail when theCD TEA of 2.6 is reached. Product “B” is the same as product “A” wherethe MD tensile has been pulled out to make the MD and CD tensile andstretch the same. The product now has equal MD and CD TEA values, hencegiving maximum utility for a given tensile strength and stretch. Butwhile the MD and CD TEA are equal, they are relatively low, giving theconsumer the perception that the product is only moderately strong. Anadditional improvement is made in product “C”, where the stretch isincreased while keeping the tensile the same as that of product “B”.This results in a product with double the TEA when compared to product“B”. More importantly, product “C” also has double the TEA of product“A” in the weaker direction.

Examples 2-42.

To further illustrate the invention, a pilot uncreped throughdriedtissue machine was configured similarly to that illustrated in theaforementioned Rugowski et al. patent and was used to produce a one-ply,uncreped throughdried bath tissue basesheet. More specifically, 100pounds of bleached northern softwood kraft fiber were dispersed in apulper for 30 minutes at a consistency of 3 percent. Similarly, 100pounds of bleached eucalyptus were dispersed in a pulper for 30 minutesat a consistency of 3 percent. The thick stock was then sent to amachine chest and diluted to a consistency of about 1 percent.

The machine chest furnish was diluted to approximately 0.1% consistencyand delivered to a forming fabric using a three-layered headbox. Theforming fabric speed was approximately 62 fpm. The resulting web wasthen transferred to a transfer fabric traveling at the same or slowerthan the forming fabric using a vacuum shoe to assist the transfer. At asecond vacuum shoe assisted transfer, the web was delivered onto athroughdrying fabric. The web was dried with a throughdryer operating ata temperature of 375° C.

Bath tissue basesheet was produced with an oven-dry basis weight ofapproximately 26 gsm. The resulting product was equilibrated for atleast 4 hours in TAPPI Standard conditions (73° F., 50% relativehumidity) before tensile testing. All testing was performed on basesheetfrom the pilot machine without further processing. The processconditions are shown in Table 2. The resulting product tensileproperties are reported in Table 3. The results are also plotted inFIGS. 4-10, previously discussed. TABLE 2 Vacuum Vacuum Vacuum VacuumVacuum TAD Emveco Ambient Headbox Fabric Fabric HB Bot HB Top DewaterTransfer 1 Transfer 2 Speed Rush Caliper BW H2O Example Transfer TAD ″Hg″H2O ″H2O ″Hg ″Hg ft/min Transfer mils gsm gpm 2 t1205-1 t1207-6 38 3710.2 9.7 9.2 50 10% 24.5 28 45.0 3 t1205-1 t1207-6 38 37 10.2 9.7 9.5 508% 23.7 28 45.0 4 t1205-1 t1207-6 38 37 10.2 9.7 9.5 50 8% 22.6 28 45.05 t1205-1 t1207-6 32 35 12.5 12 10 50 8% 21.2 28 45.0 6 t1205-1 t1207-650 55 12.2 11.5 9.5 50 8% 23.9 28 45.0 7 t1205-1 t1207-6 40 40 12.2 11.59.5 50 8% 22.2 28 45.0 8 t1205-1 t1207-6 45 45 12.2 11.5 8.7 50 14% 22.128 45.0 9 t1205-1 t1207-6 38 37 12.5 11.6 6.5 50 8% 20.9 28 45 10t1205-1 t1207-6 37 39 14.4 14 6.8 50 10% 34 45 11 t1205-1 t1207-6 36 3813.8 13.4 4.0 50 8% 19.3 28 45 12 t1205-1 t1207-6 39 40 12.6 12 4 60 8%21.1 34 45 13 t1205-1 t1207-6 39 39 13.5 13.2 4.9 50 8% 19.7 28 45 14t1205-1 t1207-6 41 40 13.2 13 4.75 70 8% 19.2 28 45 15 t1205-1 t1207-639 40 13.6 13.1 4.9 70 8% 19.1 28 45 16 t1205-1 t1207-6 38 39 13.6 13.14.9 70 10% 19 28 45 17 t1205-1 t1207-6 39 40 14.2 13.2 5 70 10% 18.6 2845 18 t1205-1 t1207-6 39 40 14.2 13.2 5 70 8% 18.2 28 45 19 t1205-1t1207-6 38 40 13.2 13.4 5.1 70 10% 18.7 28 45 20 t1205-1 t1207-6 38 4013.1 12.8 8.1 70 10% 20.1 28 45 21 t1205-1 t1207-6 38 40 12.7 12.5 10 7010% 22.5 28 45 22 t1205-1 t1207-6 38 40 12.7 12.5 10 70 10% 22 28 55 23t1205-1 t1207-6 38 40 12.7 12.5 10 70 10% 22 28 55 24 t1205-1 t1207-6 3840 12.7 12.5 10 70 10% 22.6 28 35 25 t1205-1 t1207-6 38 40 12.7 12.5 1070 10% 22.6 28 35 26 t1203-1 t1207-6 42 41 12.4 11.5 3.5 60 10% 23.1 2845 27 t1203-1 t1207-6 41 40 11.5 11 8.6 60 18% 27.2 28 45 28 t1203-1t1207-6 41 40 11.6 11 8.6 60 17% 26.9 28 45 29 t1203-1 t1207-6 41 4011.7 11 8.9 60 17% 26.3 28 45 30 t1203-1 t1207-6 41 40 11.7 11 8.9 6017% 26.3 28 45 31 t1203-1 t1207-6 41 40 11.9 11.1 9 60 16% 25.3 28 45 32t1203-1 t1207-6 39 39 11.8 10.8 9.25 60 16% 26.7 28 45 33 t1203-1t1207-6 38 39 12 11.2 9.4 60 16% 26.2 28 45 34 t1203-1 t1207-6 39 3912.2 11.2 9.4 60 16% 25.9 28 45 35 t1203-1 t1207-6 39 39 12.2 11.6 9.960 14% 24.4 28 45 36 t1203-1 t1207-6 39 39 12.6 11.7 8.4 60 14% 25 28 4537 t1203-1 t1207-6 39 39 13.4 12.5 5.2 60 14% 23.6 28 45 38 t1203-1t1207-6 39 39 12.4 11.6 11.6 60 14% 26 28 45 39 t1203-1 t1207-6 38 3912.6 11.6 11.7 60 14% 26.5 28 45 40 t1203-1 t1207-6 38 38 12.7 11.4 11.760 16% 27.1 28 45 41 t1203-1 t1207-6 39 39 12.7 11.6 11.7 60 12% 26.3 2845 42 t1203-1 t1207-6 39 39 12.7 11.6 11.7 60 12% 26.3 28 45

TABLE 3 Tensile Tensile Tensile Tensile Tensile Tensile Tensile TensileMD Dry Tensile MD Slope MD TEA CD Dry Tensile CD Slope CD TEA TensileGMT MDTEA/ Example g/3″ MDS % g/3″ g · cm/cm2 g/3″ CDS % g/3″ g · cm/cm2MD/CD g/3″ CDTEA 2 1281 4.11 3.21 498 10.37 3450 2.77 2.57 799 1.16 31417 3.74 3.29 531 10.46 3749 2.91 2.67 867 1.13 4 1322 3.46 3 562 10.63815 3.1 2.35 862 0.97 5 1340 3.17 2.85 492.82 10.04 3707 2.62 2.72 8131.09 6 1288 3.66 2.99 597.8 9.16 4582 2.81 2.15 877 1.06 7 1171.15 3.392.49 595 9.25 4532 2.9 1.97 835 0.86 8 822 6.04 3.62 695 8.75 4973 3.251.18 756 1.11 9 1053 3.71 19777 2.58 674 8.27 5121 2.95 1.56 842 0.87 101315 4.16 3.8 811 8.27 5434 3.60 1.62 1033 1.06 11 1209 3.06 2.81 8216.76 6748 2.91 1.47 996 0.97 12 1493 3.17 3.52 1011 6.39 8570 3.43 1.481229 1.03 13 1106 3.8 2.74 710 6.81 6119 2.51 1.56 886 1.09 14 995 3.482.36 621 6.47 6400 2.15 1.60 786 1.10 15 1016 3.56 2.45 785 6.42 68572.62 1.29 893 0.94 16 908.75 4.06 2.65 721 6.61 6598 2.46 1.26 809 1.0817 926.7 4.42 2.71 711.8 6.42 6709 2.35 1.30 812 1.15 18 1024 2.81 2.09733.8 5.79 7385 2.2 1.40 867 0.95 19 1098 3.09 2.52 719 5.81 6774 2.241.53 889 1.13 20 1014 3.31 2.38 734 7.19 5744 2.82 1.38 863 0.84 21907.1 3.15 2.08 580.7 7.38 5317 2.34 1.56 726 0.89 22 999.1 2.93 2.22638.4 7.65 5378 2.63 1.57 799 0.84 23 999.1 2.93 2.22 638.4 7.65 53782.63 1.57 799 0.84 24 956.1 2.74 1.93 553 7.45 5289 2.27 1.73 727 0.8525 956.1 2.74 1.93 553 7.45 5289 2.27 1.73 727 0.85 26 827.38 3.89 2.32569 8.25 4308 2.4 1.45 686 0.97 27 619 7.29 7844 3.17 535 10.7 3345 3.051.16 575 1.04 28 666 7.03 8465 3.25 632 11.31 3452 3.63 1.05 649 0.90 29686 6.62 9225 3.3 599 10.97 3512 3.43 1.15 641 0.96 30 686 6.62 9225 3.3599 10.97 3512 3.43 1.15 641 0.96 31 703 6.6 8984 3.38 622 10.9 35943.42 1.13 661 0.99 32 721 6.51 9874 3.36 574 10.68 3498 3.17 1.26 6431.06 33 666 6.72 8415 3.23 510 10.95 3216 2.89 1.31 583 1.12 34 665 6.378160 2.81 519 10.27 3402 2.71 1.28 587 1.04 35 796 5.51 9583 2.94 56410.22 3569 2.92 1.41 670 1.01 36 768 5.46 9470 2.61 621 10.28 3764 3.161.24 691 0.83 37 828 5.92 3.3 653 9.42 4269 3.06 1.27 735 1.08 38 8125.14 3.02 580.86 10.46 3313 3.17 1.40 687 0.95 39 828 5.07 2.97 59210.39 3434 3.15 1.40 700 0.94 40 775 6.17 3.39 583 11.03 3412 3.19 1.33672 1.06 41 794 4.45 2.5 551 10.19 3630 2.84 1.44 661 0.88 42 794 4.452.5 551 10.19 3630 2.84 1.44 661 0.88

Because peak tensile strength affects TEA, it would be expected thattissue with a greater MD/CD ratio would have a greater MD/CD TEA ratio.As the data in FIG. 4 show, substantially equal MD/CD TEA ratio sampleswere produced over a large range of MD/CD tensile. The relationshipbetween MD/CD tensile ratio and MD/CD TEA ratio is complex. FIGS. 4-10provide insight into the complicated relationships between tissuemachine fabrics, rush transfer levels, and tensile strength propertiesthat influence the MD/CD TEA ratio.

In general, many different factors can be manipulated to produce theproducts having an MD TEA and CD TEA which are substantially equal.These factors include the MD and CD tensile strength, the topography ofthe transfer and throughdrying fabrics, chemicals, rush/drag forming(jet-to-wire ratio), forming consistency, percent rush transfer, crepingvariables, vacuum levels, fiber species, pulping conditions,hardwood/softwood ratio, refining level and reeling (percent stretchpullout).

As the MD TEA is normally higher, emphasis must be placed onmanipulating these factors to increase the CD TEA to make itsubstantially equal to the MD TEA. How each of these factors must bemanipulated is process dependent, and adjustments may need to be madedifferently for different processes. However, some general statementscan be made about methods to generate essentially equal MD and CD TEA.

In this respect, the CD tensile strength can often be increased byincreasing the percent hardwood in the furnish. More hardwood relativeto softwood will tend to decrease the MD/CD tensile ratio, thus makingthe TEA closer to equal.

Concerning the fabric topography, the effect on MD/CD TEA is complex anddependent on several factors such as the weave pattern. For MD-orientedfabrics, increasing the fabric topography may increase CD TEA and hencemake MD and CD TEA more equal by increasing the percent stretch in theCD. However, the effect on the shape of the CD stress/strain curve mustbe considered, and hence this effect is not true for all fabric designs.

As to the jet-to-wire ratio, the MD/CD tensile ratio generally follows awell-known “U” shape as jet-to-wire is increased, reaching a minimum atsome jet to wire ratio which may be both hardware and speed dependentand increasing on either side of this point. To minimize MD/CD TEA, itis advisable to set the jet-to-wire ratio at a value which is close tothe nadir of this curve.

As to forming consistency, lowering the forming consistency willgenerally cause better formation, and hence an increase in both MD andCD tensile and thus MD and CD TEA. To determine what forming consistencyoptimizes equality of MD and CD TEA, the forming consistency can bealtered and a MD/CD TEA versus forming consistency graph generated andthe best point selected.

Concerning creping variables, those variables that increase percenttensile reduction will generally tend to make MD/CD TEA ratio moreequal. For example, greater web adhesion will cause greater MD tensilereduction during creping, and for equal stretch values will decrease theMD TEA, thus making the MD/CD TEA ratio closer to one. Of course, thisparameter would not apply to uncreped processes.

Reeling variables, such as percent stretch pull-out, are other variablesthat can be manipulated to make the MD and CD TEA values essentiallyequal. Again, since MD TEA is generally larger than CD TEA, morepull-out of MD stretch via greater reel speed will tend to make MD andCD TEA closer to equal. However, the pull-out should not be increasedbeyond the level that makes the TEAs approximately equal, lest the webbe damaged. Since the optimum performance is obtained by having the TEAsessentially equal and stretch of 5% or greater in both the MD and theCD, it is not desirable to reduce the MD stretch to less than 5% duringwinding of the web.

As an alternative to the above methods, CD TEA can be increased byaltering the process so as to place an elastomeric bonding material onthe web. The bonding material may be, for instance, an ethylene vinylacetate copolymer or other related polymers. Depending on the desiredresult, the bonding material may be applied only to one side of the webor to both sides of the web. The elastomeric material can either beapplied on the tissue machine per U.S. Pat. No. 3,879,257 to Gentile etal or in an off-line process as described in U.S. Pat. No. 6,423,180 toBehnke et al. both herein incorporated by reference. After applicationof the elastomeric material, the web may be creped if desired. Thepresence of the elastomeric material and the pattern utilized for theapplication of the elastomeric material can give increased CD stretch,increased CD TEA and therefore substantially equal MD and CD TEA.

It will be appreciated that the foregoing examples and discussion, givenfor purposes of illustration, are not to be construed as limiting thescope of this invention, which is defined by the following claims andall equivalents thereto.

1. A tissue sheet having a three-dimensional surface topography, an MD/CD TEA ratio of from about 0.8 to about 1.2 and a CD stretch of about 5 percent or greater.
 2. The tissue of claim 1 wherein the MD/CD TEA ratio is from about 0.9 to about 1.1.
 3. The tissue sheet of claim 1 wherein the geometric mean tensile strength is about 1500 grams or less per 3 inches of width.
 4. The tissue sheet of claim 1 wherein the geometric mean tensile strength is about 1200 grams or less per 3 inches of width.
 5. The tissue sheet of claim 1 wherein the geometric mean tensile strength is from about 500 to about 1200 grams per 3 inches of width.
 6. The tissue sheet of claim 1 wherein the geometric mean TEA is about 20 gram-centimeters or less per square centimeter.
 7. The tissue sheet of claim 1 wherein the geometric mean TEA is about 10 gram-centimeters or less per square centimeter.
 8. The tissue sheet of claim 1 wherein the geometric mean TEA is from about 2 to about 8 gram-centimeters per square centimeter.
 9. The tissue sheet of claim 1 wherein the geometric mean TEA is from about 2 to about 4 gram-centimeters per square centimeter.
 10. The tissue sheet of claim 1 wherein the MD stretch is about 3 percent or greater.
 11. The tissue sheet of claim 1 wherein the MD stretch is about 5 percent or greater.
 12. The tissue sheet of claim 1 wherein the MD stretch is from about 3 to about 30 percent.
 13. The tissue sheet of claim 1 wherein the MD stretch is from about 3 to about 25 percent.
 14. The tissue sheet of claim 1 wherein the MD stretch is from about 3 to about 15 percent.
 15. The tissue sheet of claim 1 wherein the MD stretch is from about 3 to about 10 percent.
 16. The tissue sheet of claim 1 wherein the CD stretch is from about 5 to about 20 percent.
 17. The tissue sheet of claim 1 wherein the CD stretch is from about 5 to about 15 percent.
 18. The tissue sheet of claim 1 wherein the CD stretch is from about 5 to about 10 percent.
 19. The tissue sheet of claim 1 wherein the CD stretch is greater than the MD stretch.
 20. A tissue sheet having a three-dimensional surface topography, an MD/CD TEA ratio of from about 0.8 to about 1.2, a CD stretch of about 5 percent or greater, an MD stretch of about 5 percent or greater and a geometric mean tensile strength of about 1500 grams or less per 3 inches of width.
 21. The tissue sheet of claim 20 wherein the geometric mean TEA is about 20 gram-centimeter or less per square centimeter.
 22. The tissue sheet of claim 20 wherein the geometric mean TEA is about 10 gram-centimeter or less per square centimeter.
 23. The tissue sheet of claim 20 wherein the geometric mean TEA is from about 2 to about 8 gram-centimeter per square centimeter.
 24. The tissue sheet of claim 20 wherein the geometric mean TEA is from about 2 to about 4 gram-centimeter per square centimeter. 